1. Field of the Invention
The present invention relates to air quality control systems, and more particularly, to air quality control systems useful with electric arc furnaces for melting steel in steel casting operations.
1. Description of the Prior Art
Electric arc furnaces are well known in the steel foundry art. Such furnaces typically employ a large covered crucible for melting steel. Molten steel is then poured through a furnace spout from the crucible to a ladle, for example, that may deliver the molten steel to a mold where the molten steel is poured from the ladle to make a steel casting.
In such furnaces, a group of electrodes are typically introduced into the crucible through openings in the furnace roof. These electrodes serve to heat the contents of the crucible to the desired temperature. The body of the crucible usually has several other openings, for various purposes. A door, such as a back door, is provided for the foundry person to check on the state of the molten material, for insertion and operation of various tools, such as an oxygen lance into the interior of the crucible, and for charging the material with additional ingredients. A pebble lime intake pipe is also included in such furnaces for introduction of pebble lime into the crucible. The roof has three openings through which the electrodes are inserted and removed for heating the metal within the crucible. The furnace also has a spout for tapping molten metal out of the furnace when desired.
To tap the molten steel from the furnace, the entire furnace must be tilted. When the furnace is tilted, the roof of the furnace and the electrodes move through an arc so that the molten metal will flow through the spout.
Use of such furnaces typically results in the generation of fumes, which can exit the furnace from different openings at different times, and in different concentrations at different phases of the process. For example, during melting of the scrap steel, fumes may emit from the roof openings at the electrodes, at the juncture of the roof and the crucible, and through the door. During tapping of the molten steel, the majority of the dust and fumes may be emitted from the vicinity of the spout, with smaller quantities escaping from the electrode roof holes and door. Dust and fumes may also be generated at other sites outside of the typical steel casting facility, such as at the bag house.
One standard air quality control system for use in such environments comprises a canopy hood that draws fumes from the entire plant environment above the furnace into an exhaust duct, and drawing the collected fumes and air to a bag house, where the fumes and air are filtered though bags for removal of particulate. However, to collect and process all of the air in the vicinity of the furnace, is costly to operate: the fan that draws the air must have a motor sized to pull a large quantity of air through the system, and it must be run for extended periods of time, using great amounts of energy at great costs. In addition, an overhead canopy does not necessarily protect the workers in the furnace area from the dust and fumes generated, since the workers are typically between the emissions source and the canopy and may be exposed to the fumes and dust that passes up to the canopy.
In some other prior art furnaces, hoods and a duct moving with the furnace were mounted to the roof of the furnace. This duct mated with stationary duct work only when the furnace was upright and was connected to a collector and fan to draw fumes from the furnace, but the hoods were rendered ineffective when the furnace was tilted to tap the molten metal; when the furnace was so tilted, the ducts became disconnected so that emissions from the furnace escaped to the plant, and so that the duct leading to the collector either drew air from the plant instead of from the furnace or was closed off so as to be ineffective.
In the bag house, air has been drawn through the filter bags, where the particulate has been collected and then dropped into receptacles for disposal. However, the collected particulate is frequently a fine powdery substance, easily dispersed into the environment when dropped into the receptacle.